This invention relates to document information filing systems for storing document information in unit information after another in a recording medium and retrieving for and reading out desired document information.
Recently, document information filing systems have been developed and put to practical use. According to such document information filing system, each of a great deal of documents or the like is scanned by a scanner to produce document information which are progressively stored in a storage device. The desired document information among the various document information stored in the storage device is retrieved and read out for being reproduced into a visual state by an output device such as a cathode-ray-tube (CRT) display or a copying device.
In such document information filing system, the recording medium has a definite storage capacity (for instance about 3,000 A4 size documents in case of a magnetic tape). It is sometimes desired to know the remaining document information storage capacity of the recording medium when it is intended to record new document information.
However, in the document information filing system of the aforementioned kind, document information is recorded in the recording medium after compressing it through the modified Hofmann coding (hereinafter referred to as MH coding) for reducing the redundancy. Therefore, the quantity of image information recorded varies with the unit document information so that it is very difficult to determine the remaining document information storage capacity on the basis of the fixed storage capacity as mentioned.